I highly recommend Eric Hoffer's The True Believer if you're interested this topic at all. It's a short book full of major ideas.

Hoffer's treatment of the phenomenon is just as fresh and relevant today as it was when he wrote the book in the 1950s.

I got downvoted for suggesting that Maoism was a religion, but it quite clearly had more commonalities than differences with the more extremist religious cults (as did Stalinism, Nazism, etc.)